Photolithography is widely used for patterning photoresist material in the production of semiconductor devices. It is desirable to perform photolithography with light of a small wavelength to allow a reduction in the design rule to create smaller semiconductor devices. For example, 193 nm lithography using an Argon Fluoride (ArF) light source may be used to obtain 0.1 μm to 0.07 μm sizes. After a pattern of photoresist material has been provided on a wafer, the exposed layer of the wafer can be etched.
A large number of different chemicals and combinations of chemicals have been used in the past to provide active species in a plasma for etching wafers. There is a complex interplay between the composition of the etchant gas, the material being etched, and the operating conditions of the plasma processing device in which the etching is carried out. Different species of the plasma can be active in providing different effects on the wafer being processed. Hydrogen bromide has been used in the past as an etchant for etching a polysilicon layer in a wafer, with the bromine species in the plasma being active in etching the polysilicon material.
However, etching can have deleterious effects on the fabrication of devices from the wafer. For example, the photoresist material itself can be substantially removed which can expose the area that the photoresist is intended to protect. Also the etchant can cause the photoresist material to deform or twist, which in turn causes the features resulting from etching to be deformed. For example, the intended feature of a straight track could be well defined by photoresist material. However, etching to define the actual track can result in a wavy track actually being formed owing to the twisting and deformation of the photoresist material caused by the etching mechanism. The inability to control the shape of the features being etched can result, in the worst case, in device failure, or at least in non-reproducibility.
In view of the foregoing, it is desirable to be able to use a low wavelength photoresist material for defining features which are well reproduced by an etch process.